The purpose of this project is examination of mechanisms of regulation of calcium metabolism during pregnancyy and in the perinatal period, with special emphasis on endocrine factors. Both humans and nonhuman primates (rhesus monkeys) will be studied. The hormones parathyroid hormone and calcitonin will be measured by immunoassay throughout pregnancy, in fetal serum in late pregnancy, and in neonatal serum shortly after birth. Baseline levels and response to provocative stimuli will be determined and relationships between these hormones and total and ionic calcium, inorganic phosphorous, and protein levels assessed. These studies will provide information regarding (1) the normal maternal physiologic adjustments regulating calcium levels during pregnancy, (2) any deviations from the normal pattern in abnormal pregnancy, (3) the relationships between maternal and fetal calcium metabolism, (4) fetal endocrine regulation of its own calcium metabolism, (5) normal regulatory adjustments during the early neonata period and (6) how these adjustments may, under special circumstances, relate to neonatal hypocalcemia.